Boeing C-17 Globemaster III

Mission

The Boeing C-17 Globemaster III is capable of rapid strategic delivery of troops and cargo to main operating bases, or directly to forward bases in the deployment area. The aircraft is also able to perform tactical airlift and airdrop missions when required. The inherent flexibility and performance characteristics of the C-17 force improves the ability of the total airlift system to fulfill the worldwide air mobility requirements of the United States.

Background

In December 1979, the Department of Defense initiated the Cargo-Experimental (C-X) competition to identify a new jet-powered strategic airlifter incorporating exceptional field performance capabilities, a cabin offering large-volume capacity, and a rear loading assembly to accommodate wheeled or tracked vehicles. Also, the aircraft must be capable of airlifting or airdropping outsize loads, including armored vehicles, directly into a combat zone.

Boeing (then McDonnell Douglas) was selected as the prime contractor in August 1981. However, the full-scale engineering and development contract was not signed until December 1985. The winning design, designated the C-17 Globemaster III, incorporated many features proven earlier on the YC-15, a McDonnell Douglas aircraft developed and flight tested in the 1970s as part of the Advanced Medium Short Takeoff and Landing Transport (AMST) program.

The C-17 program was restructured in 1990 following the OSD Major Aircraft Review, reducing the planned buy from 210 to 120 aircraft. After several delays, the first C-17A (T-1 #87-0025) successfully accomplished its maiden flight on 15 September 1991, and deliveries to the 17th Airlift Squadron (AS) at Charleston AFB, SC began on 14 June 1993. On 17 January 1995, the squadron was declared operationally ready. The 14th and 15th Airlift Squadrons soon followed as the wing continued to receive new Globemaster IIIs. Eight C-17s have been delivered to the 97th Air Mobility Wing at Altus AFB, OK, where initial aircrew training occurs. McChord AFB in Tacoma, WA is now receiving new C-17s. McChord's 62nd Airlift Wing will receive 48 of the versatile airlifters, which will also be operated by McChord's reserve unit, the 446th Airlift Wing. The Air National Guard unit in Jackson, MS, will also receive C-17s in the future.

The C-17 is possibly the most flexible airlift aircraft to enter the Air Force inventory since the C-130 Hercules. The ultimate measure of airlift effectiveness is the ability to rapidly project and sustain an effective combat force close to a potential battle area. Threats to U.S. interests have changed in recent years, and the size and weight of U.S. mechanized firepower and equipment have grown in response to the improved capabilities of potential adversaries. This trend has significantly increased air mobility requirements, particularly in the area of large or heavy outsized cargo. As a result, additional airlift is needed to meet potential armed contingencies, peacekeeping or humanitarian missions worldwide.

Since 1995, the fleet has amassed more than 250,000 flying hours. The C-17 has been involved in numerous contingency operations, including flying troops and equipment to Operation Joint Endeavor to support peacekeeping in Bosnia and Allied Force Operation in Kosovo. In 1998, eight C-17s completed the longest airdrop mission in history, flying more than 8,000 nautical miles from the United States to Central Asia, dropping troops and equipment after more than 19 hours in the air, a feat repeated in 2000.

Features

The C-17 incorporates many of the military jet transport standards — a high-set wing (swept 25 degrees), T-tail, rear cargo-loading assembly and heavy-duty retractable landing gear with fuselage blister fairings. The aircraft also features a state-of-the-art "glass cockpit" (with four multi-function displays and a HUD for each pilot), a GEC fly-by-wire control system (featuring a stick rather than the conventional yoke), four high-performance turbofan engines, an advanced supercritical wing section, winglets, and a "blown-flap" system. Maximum use has been made of off-the-shelf and commercial equipment, including Air Force-standardized avionics. The aircraft is operated by a crew of three (pilot, co-pilot and loadmaster).

With a payload of 160,000 pounds, the C-17 can take off from a 7,600-foot airfield, fly 2,400 nautical miles, land on a small austere airfield in 3,000 feet or less. It can be refueled in flight.

Cargo Compartment - Capacity: 18 fully-loaded 463L-type cargo pallets (88" x 108" @ 10,000 pound (4,536kg) capacity); up to 40 containers for Container Delivery System (CDS) airdrops; 102 troops; 48 litter and 54 ambulatory patients and attendants; three AH-64A Apache helicopters; one main battle tank; three Bradley armored vehicles. (A combination of pallets and wheeled vehicles can be carried together when required.)
Able to accommodate nearly 100 percent more cargo volume than the C-141B Starlifter, the C-17 can carry virtually all of the Army's air-transportable, outsized combat equipment. It is also able to airdrop paratroopers and cargo. All cargo is loaded through a large ramp/door assembly in the rear of the aircraft.

Engines - The C-17 is powered by four fully-reversible Pratt & Whitney PW2040 series turbofans, designated as F117-PW-100 by the Air Force. Each engine is rated at 40,440 pounds (180kN) of thrust and employ thrust reversers that direct the flow of air upward and forward to avoid ingestion of dust and debris.

Supercritical Wing - Like other military transports, the C-17 uses a "supercritical" wing. These are advanced airfoil designs that enhance the range, cruising speed, and fuel efficiency of jet aircraft by producing weaker shock waves that create less drag and permit high efficiency.

Winglets - In the mid-1970s, the NASA-Langley Research Center developed the winglet concept through wind tunnel research. Winglets are small, wing-like vertical surfaces at each wingtip of an aircraft that enable the airplane to fly with greater efficiency. They curve flow at the wingtip to produce a forward force on the airplane, similar to the sail on a sail boat. Each C-17 winglet spans 9 feet, 4 inches.

Powered Lift & STOL Capability - A key element of the C-17 is the special flap system, first developed by a team of researchers at NASA-Langley in the mid-1950s and later demonstrated on the YC-15 prototype. The externally "blown-flap" or "powered-lift" system enables the aircraft to make slow, steep approaches with heavy cargo loads. With this powered-lift system, the engine exhaust flow is directed below and through slotted flaps to produce additional lifting force and allow steeper landing descents.
Short TakeOff and Landing (STOL) capability is achieved when the trailing-edge flaps are extended into the exhaust flow from the engines during takeoffs and landings. The engine exhaust is deflected downward by the slotted-flaps to augment the wing lift. This allows aircraft with "blown flaps" to operate at roughly twice the lift coefficient of that of conventional jet transport aircraft.
The C-17 can operate on small, austere airfields with runways as short as 3,000 feet (914m) and as narrow as 90 feet (27.4m) wide, and can complete a 180-degree three-point "star" turn within 80 feet (24.4m). Also, when fully loaded, the aircraft is capable of backing up a 2 percent gradient slope using the directed flow thrust reversers.

Composite Materials - Sixteen-thousand pounds of composite materials have been applied to the C-17. Several of the major control surface and secondary structural components of the aircraft are made of composites. The most direct contribution to C-17 applications was the development of the DC-10 graphite-epoxy upper aft rudders. These rudders have accumulated more than 500,000 flight hours since they were introduced into regular airline service in 1976. The high-time rudder alone has flown for 75,000 hours. The control surfaces of the C-17 follow the same multi-rib configuration as the DC-10 rudders.

Landing Gear - The C-17's landing gear system consists of a single nose strut with two wheels and two twin-strut tandem gear assemblies, one per side with three wheels per strut. The aircraft can takeoff or land just about anywhere in the world.

Missile Warning & Fare Dispensing - The C-17 is equipped with Tracor AN/ALE-47 countermeasure flare dispensers and the Lockheed Martin/Alliant Techsystems AN/AAR-47 missile warning system.
The AN/AAR-47 is a passive missile warning system with a suite of surface-mounted thermal sensors around the aircraft which detect the thermal signature of the missile exhaust plume. Frequency selection and signal processing techniques are used to minimize the "false alarm" rate. The system provides a warning to the crew, via the cockpit indicator unit, of the presence and direction of the missile threat. A signal is automatically sent to the ALE-47 countermeasures dispenser.
AN/ALE-47 is capable of carrying a mix of expendable countermeasures including jammers. The system directly interfaces with the aircraft's sensors. The aircrew can select the mode of operation of the dispenser for fully automatic, semi-automatic or manual operation. The cockpit control unit can be used to input mission data together with the numbers and types of expendable countermeasures systems loaded into the ALE-47. The cockpit controller updates and displays the status of the dispenser and the numbers and types of countermeasures remaining. The ALE-47 is capable of dispensing the new generation active expendable decoys POET and GEN-X in addition to the conventional chaff and flare decoys which are compatible with the previous generation ALE-40 and ALE-39 dispensers.

Service Life

Based on a buy of 120 aircraft, the last C-17 will be delivered in November 2004. The original specification from McDonnell Douglas defined a service life of 30,000 hours. Modification programs will keep the aircraft in line with current and future requirements for threat avoidance, navigation, communications, and enhanced capabilities. These modifications should include global air traffic management (GATM) and automatic dependent surveillance to meet anticipated navigation requirements. Commercially available avionics and mission computer upgrades are being investigated to reduce life-cycle costs and improve performance. Also, upgraded communication systems to enhance worldwide voice and data (including secure) transmission will support command and control.

Records

The C-17 currently holds over 20 world-class airlift records, including payload to altitude time-to-climb, and the Short TakeOff and Landing (STOL) mark in which the C-17 took off in less than 1,400 feet (427m), carried a payload of 44,000 pounds (19,958kg) to altitude, and landed in less than 1,400 feet (427m).

In 1998, eight C-17s completed the longest airdrop mission in history, flying more than 8,000 nautical miles (14,816km) from the United States to Central Asia, then dropping troops and equipment after more than 19 hours in the air.